This invention relates to a bit attaching arrangement for a power tool, and, more particularly, to an arrangement that allows the bit to be attached without the use of external wrenches or keys.
Power tools, such as routers, often incorporate a collet for holding the shank end of a bit in place on the lower end of a rotating armature/output shaft. In particular, the collet consists of a generally cone-shaped structure having a split end which defines separate prongs which are usually biased slightly radially outwardly. The end of the collet opposite the prongs is generally attached to or formed integrally with the output shaft of the router. A collet locking nut is used to secure a bit onto the output shaft. The collet nut has a female thread surface which engages a male thread surface located on the lower end of the output shaft. The collet nut fits over the collet and has a female cone-shaped camming surface for engaging the cone-shaped outer surface of the collet.
In order to attach a bit to a router utilizing this well-known structure, the shank of the bit is positioned between the prongs of the collet with the collet nut in a loosened position on the output shaft. After the shank of the bit is completely disposed within the hollow output shaft, the collet nut is tightened such that the prongs of the collet engage the side surfaces of the shank and firmly hold the bit in place on the lower end of the shaft. In order to sufficiently tighten the collet nut so as to secure the bit, external and separate tools and/or wrenches are typically utilized. In particular, the tightening operation of this prior art structure often involves utilizing a shaft lock arrangement which prevents rotation of the output shaft of the router and thereafter manually tightening the nut using a dedicated individual wrench which is often included with the router when it is sold.
This prior locking arrangement suffers from numerous disadvantages. First, because the tightening wrench is a separate item, it is often lost or misplaced after the router has been used for a period of time. This often results in an operator utilizing a non-dedicated wrench or pliers to tighten the collet nut. Use of the incorrect sized wrench or pliers may result in damage to the collet nut and/or locking arrangement. Additionally, use of a non-dedicated wrench can also result in the collet nut not being sufficiently tightened causing slippage between the bit and the output shaft.
A further disadvantage is the amount of time it takes to replace a router bit. More specifically, to adequately tighten the collet nut, it requires numerous placement and replacement of the wrench on the collet nut to tighten the nut. This is due to limited access to the attaching arrangement through the guards and support plates of the router. Still further, as mentioned above, to rotate the nut with respect to the output shaft, there oftentimes is a shaft locking mechanism disposed internally within the assembly. This can result in a further disadvantage because of the possibility of the shaft locking mechanism malfunctioning and impeding the rotation of the output shaft. Another disadvantage of utilizing an internal spindle lock is that typically the lock will only prevent the output shaft from rotation when the shaft is at predetermined rotational locations. In particular, there are indentations in the shaft which are engaged by the lock and an indentation must be aligned with the lock mechanism before the shaft can be secured.
Therefore, a bit locking arrangement is needed which will overcome the problems discussed above.